Re: Was TOS the first show to use the term 'parallel universe'?
Gerry Anderson did a live action film that ran under different titles, The Doppelgangers
aka Journey to the Far Side of the Sun
. Don't remember what they called it then, thought it was supposed to be a physical world, not alternate universe I think.
Dr. Howard, Dr. Fine, Dr. Howard: For duty and humanity! --Men in Black (1934)